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Also, you're probably missing the hardware requirements to capture the actual packets (unless you got a hold of a fancy custom firmware). You need an old hub or managed switch with port mirroring on any end where ALL data packets come together, and connect your laptop with Wireshark before you can even start decoding the packets.

Situation 1:
It's a modem router, there's no WAN port (but directly to the phone line/ADSL). You can't capture Wifi! You need an extra switch besides the old hub or managed switch that I mentioned before. Connect all LAN cables to this switch, then a cable to the old hub or managed switch. Then a cable to the TPLink. Your laptop will be connected to the hub/managed switch
Situation 2:
It's a "normal" router with wifi. Connect WAN from TPLink to your hub/mananged switch, from there connect to the original location (probably modem). Connect laptop to hub/managed switch.

Wireshark is the go-to tool for capturing packets, either on LAN or WAN, it won't give you the passwords or chat messages in a clear to see way but you can use filters to optimize it, more info to use Wireshark on WiFi: http://wiki.wireshark.org/CaptureSetup/WLAN

There's also loads of videos and howto's out there on using Wireshark to capture traffic.

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If your IM client requires SSL/TLS, try using an SSL MiTM proxy, such as Burp Suite, Fiddler, or Charles. Succeeding may depend on whether or not the IM client will inherently trust untrusted certs, or is configurable to do so.

Depending on the IM client, different approaches may be required-- for example Lync.

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lexmark1Author Commented: 2014-04-19

Thanks for all participators,
In deed I used a Cisco switch and connect my laptop to the mirror port also I used Wfilter software to track users I can see websites and web mail but not whatsapp and viber chatting also I am unable to see passwords.

Ok good to know. But those are indeed secured traffic. I'm not even sure is it's basic SSL/TSL, or if there's an extra own encryption layer above it (like Skype used to have). As stated above, if you try any man in the middle attack, you risk breaking the client (and if not, probably a big warning sign which might frighten the user into continuing his session).
And if an extra encryption layer is used, you might need months if not years to crack it.